The invention is directed to a chemical system of gas evolving oil viscosity diminishing compositions (GEOVDC) for stimulating the productive layer of an oil reservoir, that is to chemical compositions for a thermochemical treatment of an oil reservoir, more specifically for initiating a chemical reaction in the productive layer zone of the oil reservoir to produce heat and evolve gases so that the extraction of oil (petroleum) is improved. The invention is further directed to a method of thermochemically treating an oil reservoir by means of this chemical system, and to an apparatus for performing thermochemical treatment of an oil reservoir.
The extraction of petroleum from an oil reservoir usually starts with recovery methods using underground pressure in the oil reservoir which will force the oil to the surface. Over the lifetime of the oil well the pressure decreases, and it becomes necessary to use other extraction methods such as using pumps or injecting water, natural gas or other gases into the oil well to bring the oil to the surface. After recovery methods are no longer effective the oil reservoir usually still contains considerable amounts of petroleum being enclosed in small cavities or pores of the rock or sand formations.
To recover the remaining amounts of petroleum tertiary oil recovery methods are used which mainly have the aim to reduce the viscosity of the petroleum. One common method is to inject hot steam into the oil well to heat the petroleum and thus to reduce its viscosity. This method, however, is efficient only up to a depth of about 1 km as otherwise the hot steam will be cooled down before reaching the pay zone. Further, with this method up to 3 to 5 months of injecting hot steam are necessary to heat up the pay zone. Alternatively, surfactants or solvents can be injected into the oil well to leach out the petroleum. Such methods however, have the disadvantages that the extracted petroleum will be contaminated by chemicals so that additional efforts and costs are necessary to recover the petroleum.
Another tertiary oil recovery method is characterized in that a chemical reaction is initiated in the pay zone of the oil reservoir to produce hot gases which heat up the oil in the pay zone to reduce its viscosity and to support oil recovery by increasing the pressure in the oil well.
Disclosed in Russian patent applications RU 2100583 C1, RU 2126084 C1 and RU 2153065 C1 are fuel and oxidizing compositions (FOC) which are able to produce hot gases after initiating a chemical reaction. FOC are intended to be introduced into the oil well of an oil reservoir for a thermochemical treatment of the pay zone. The chemical compositions are aqueous solutions containing large amounts of up to 60% by mass or more of ammonium nitrate, NH4NO3. The other components of FOC are for instance glycerin, nitric acid, carbamide, potassium permanganate, acetic acid, isopropyl metacarborane and acetylsalicylate. After injection of the FOC into the oil well it is ignited by initiating a fuse explosion. The decomposition of 1 kg of FOC results in emitting a quantity of heat of about 500-1000 kcal.
FOC contain an excess of oxygen and hence have a substantial oxidizing character, so that with the admixture of petroleum an explosive composition is created. Further, aqueous solutions containing large amounts of ammonium nitrate are explosive if the water content is below a critical amount of about 16-18% by mass. Hence, in view of safe handling of such compositions the water content is usually above 26-28% by mass. However, with increasing water content it becomes more and more difficult to achieve a stable reaction with a high output of heat.
In Russian patent application RU 2194156 C1 the FOC contains mainly the reaction product of nitric acid with an alkanolamine, alkyl amine or alkyl polyamine and up to 2.0 to 35.0% by mass of an inorganic nitrate such as ammonium nitrate, potassium nitrate, sodium nitrate or calcium nitrate. With such a composition safer handling was achieved as the amount of ammonium nitrate could be reduced substantially. However, with the usual way of igniting the FOC by means of a fuse explosion, for safety reasons a maximum mass of only 1 to 2 tons can be ignited. After decomposition of the FOC feed with a mass of 1 to 2 tons the whole operation of the FOC delivery and initiating charge insertion has to be repeated so that at an oil well with a depth of 1 to 2 km not more than about 10 tons of FOC can be reacted per day. If the oil well depth is about 3 to 4 km the amount of FOC to be reacted per day with this method decreases to about 5 tons. Hence, the extent of heating the pay zone and thus the efficacy of this method is limited.
It is therefore the object of the present invention to provide improved materials and an improved method to overcome the limitations of the prior art by considerably increasing the amount of heat generated in the pay zone of an oil well and thus allowing a profitable exploration of oil reservoirs. A further object of the present invention is to provide an apparatus for performing thermochemical treatment of an oil reservoir.